Stoker



' Oct. 3, 1944.

UNIT

I w. M. SCHWEICKART ETAL ,4

STOKER Original Filed Aug. 28, 1937 12 Sheets-Sheet l t M N ATTOR NE Y5 Oct. 3, 1944. w, M. SCHWEICKART EIAL 2,359,445

STOKER Original Filed Aug. ,28, 1937 12 Sheets-Sheet 2 1 Oct. 3, 1944- 'w. MQSCHWElCKAR'i' ET AL, 2,359,445

STOKER INVENTORS lama ATTORNEYS IZ'Sheets-Sheet 3 Original Filed Aug. 28, I937 1944- W.'M. SCHWEICKART ET AL 2,359,445

STOKER Original Filed Aug. 28, 1937 12 Sheets-Sheet 4 INVENTORJ WW 1M 1 9 BY m, (5 W Anonwsvs Oct. 3, 1944. w, SCHWEICKART ETAL STOKER l2 Sheets-Sheet 5 Original Filed Aug. 28, 1937 INVENTORS ATTOR NE Y5 Oct. 3, w. M..-SCH WElCKART El'AL STOKER Original Filed Aug. 28, 1937 12 SheetsSheet 6 INVENTOR5 lulu M.

ATTORNEYS Oct. 3, 1944.

W. M. SCHWEICKART ETAL STOKER Original Filed Aug. 28, 1937 12 Sheets-Sheet 7 I N VE N TORS ATTORN E Y5 Och 1944- w. M. SCHWEICKART ETAL I 5 STOKER 12 Sheets-Sheet 8 Original Filed Aug 28, 1957 INVEA TORS imam, HM

ATTORNEYS Oct. 3,1944. w. M. SCHWEICKART firm. I 2,359,445

STOKER I Original Filed Aug; 28, 1937 12 Sheets-Sheet 9 I Illl/l INVENTORS 26.9 -70%. /z

2:; @99 BYM, 2 W

ATTORNEYS w. M. SCHWEICKART ET AL 2,3 9,445

'STOKER Oct. 3, 1944.

Original Filed Aug. 28, 1937 12 Sheets-Sheet 11 Oct. 3, 1944.

W. M. SCHWEICKART ETAL STOKER Original Filed Aug. 28, 1957 l WW 5:

12 Sheets-Sheet 12 INVENTORS M44 H A'II'TORNEYS Patented Oct. 3,

} STOKEB William M. Schweickart Euclid, Ohio,

and Fred G. Julyan,

assignors to Pocahontas Fuel Company Incorporated, New York, N.Y., a corporation of Virginia Original applicationjAugust 28, 1937, Serial No. 161,494. Divided and this application March 14, 1941. Serial No. 383.432

' 29 Claims. (01. 110 -45) This invention relates to improvements in automatic coal burners.

A primary feature of this invention is the provvision of aburner that will burn different types of coking coal emciently and economically, in small domestic installations as well as in larger furnaces, and which is adapted to utilize various sizes of coal down to slack.

An important characteristic of the burner is the provision of improved means for translating the horizontal coal feed into upward feed at the bottom of the burner, avoiding any zone of high pressure at'this point.

The burner is arranged to provide a novel combustion zone properly related to the feed so as to assure efiicient coking, ignition and combustion of the solid and gaseous components without danger of back coking or clinker formation atv points that would interfere with the coal feed and efficient combustion, arranged moreover to avoid the back flow of gas under appropriate operating conditions.

Another object is to provide a burner that will have high combustion efiiciency, particularly when burning bituminous. coal. The burner is arranged to produce a relatively thin bed of burning fuel, and to eliminate difficulties with clinker formation and ash accumulation which would tend to interfere with proper combustion.

The ash removal mechanism removes the ashes and small clinkers rapidly and uniformly without interference with the fire bed, conveying them continuously to an ash discharge.

Another purpose is to improve the efliciency and. control of the air supply to the fire. The forced draught is introduced in a zone at the top .with' the coal fora variable short distance and r of the retort and outward over the grate, and is provided with an adjustment to meet the conditions'of each installation as well as the varying fusion points and other characteristics of combustion of different types of coal. Under banking conditions provision is made for independent regulation of the air drawn by natural draught, permitting the eflicient and certain maintenance of a suitable fuel bed.

A further object of the invention is to provide an effective dependable feed system for the coal from a bin collector to the retort where the coking and burning takes place. The conveyor receiving the coal from the bin collector conveys the coal faster than it is supplied by the collector and the supply of coal in the conveyor tube is thus stretched out and only partially fills the tube. At the delivery end of the conveyor where it enters the retort, the conveyor tube is filled we find that the conveying pressure of the coal in the partially filled tube is amply suflicient to maintain the tube full at the discharge end.

An important object is to provide apparatusembodying features set forth herein which is simple, compact, strong, suitable for installation under widely varying conditions and economical in operation.

other objects and advantages of the invention will appear from the following description considered in connection with the accompanying drawings in which,

Fig.1 is a perspective view of the stoker with the bin collector omitted;

Fig. 2 is a side elevation of the drive unit;

,Fig. 3 is a plan of said unit with parts in section and broken away;

Fig. is a transverse vertical section on line 4-4 of Fig. 3;

Fig 5 is a detailed side elevation of the grate drive;

. Fig. 6 is a fragmentary view of the gas collecting and return structure;

Fig. 7 is a longitudinal vertical section through the burner;

Fig. 8 is a plan view of the burner with parts broken away;

Fig. 9 is a side elevation of the burner with parts broken away;

Fig. 10 is a fragmentary side view showing the mounting of parts of the grate mechanism;

Fig. 11 is a fragmentary vertical section on line lI-H of Fig. 8 showing the air feed and the grate drive;

Fig. 12 is a fragmentary side elevation of the blower and airncontrol from the right-hand side of Fig. 4;

Fig. 13 is a central section through the ash elevator in a plane parallel to the ash removal screw with the discharge head rotated to show the discharge spouts;

Fig. 14 is a fragmentary section of the base of the ash elevator structure on line l4l| of Fig. 46

Fig. 15 is a view .similar to Fig. 7 showing a V modified for'm'ofiburner; and

in the coal bin and supplies coal to the coal feed tube 22 in which is positioned the coal screw rocker arm I I 2.

The intermittent movement of ratchet II4, which in the form shown is actuated twice during each revolution of sprocket 90, is suitably transmitted to the ashvgrate, as by eccentric I24 mounted on ratchet H4 and carrying eccentric strap I25 on connecting rod I26 which may be connected to shaker rod I09 by a suitable shock absorbing arrangement. For this purpose rod I26 may terminate in frame I21 in which the spring cage I28 is mounted, including end flanges I29 in which'shaker rod I09 is slidably rrounted, between which flanges shock absorber spring I30 is set under initial compression and maintained in compressed condition-by compression collar I3I held in suitable position on rod I09. by stop pins I33 projecting fromishaker rod I09 in position to engage the adjacent flange I29 and collar I3I under pressure of spring I30. Collar I3I is .held against rotation by engagement with cage I28, and operates through clamp screw I32 to hold rod I09 in adjusted rotated position.

ing a balanced thrust from opposite directions Cage I28 is preferably mounted removably on frame I21 as by screws I34. This shaker rod spring construction I30 will allow the stoker to run even though the grates are jammed, the rest of the mechanism continuing to function normally and the placing of the absorber spring I30 under initial'tension is important to quiet operation.

This rotary grate structure surrounds an inner retort of the burner unit C of the type in which the coal is forced upwardly through the bottom of the burner retort or pot structure, burning in the'upper portion thereof and traveling over the edge onto the great structure through which the ashes pass. In the arrangement disclosed in Figs. 1-10 the section of the coal feed tube 22 extending from the drive unit base 12 is clamped in the burner body I50 and supplies coal to the throat I5I at the bottom of the fire pot I52, which preferably is tapered outwardly from throat I5I.

The lower portion of pot I52 may consist of a pot wall I53 integral with burner body I50, and a frusto-conical pot liner I54 having a smooth, preferably enameled inner surface, fitting within wall I53 and resting on a suitable ledge I55 to provide a smooth continuation of the surface of throat I5I.

A principal problem'in feeding coal to thebottom of burners of this type is presented by the difliculty hitherto encountered in forcing the coal slowly upward at right angles to the horizontal feed tube. The tendency of the feed screw is to force the coal against the surface in line with the end of the feed tube tending to produce a packed mass of coal at this point which greatly increases the resistance to the feed screw and introduces serious problems in providing feed screw'bearings and suitable pot throat contours, and aggravates greatly the tendency of such mechanisms. to become jammed by even slight increased resistance to the travel of the coal.

In the form specifically illustrated these objections are. overcome by providing a pocket I56 extending beyond throat I5I concentric with the axis of coal feed screw 2I, and mounting in pocket I56 .a reverse screw I51. Feed screw 2I preferably terminates at a point in throat I5I slightly spaced in advance of the pot axis, and reverse screw I51 preferably terminates some distance on the opposite side of said axis, providsubstantially at the center of pot I52. In practlce' with feed and reverse screws approximately 2%" in diameter the ends of the screws are separated by 1" to 1 /2".

For drive purposes reverse screw I51 may be tubular and connected to the adjacent section of feed screw 2| by connecting shaft I58. A suitable bearing I59 mounted on the burner body I50 atthe end of pocket I56 provides a suitable journal for the terminal shaft I60 rigidly mounted in reverse screw I 51, the arrangement being such that terminal shaft I60, reverse screw I51, connecting shaft I58, and coal feed screw 2I consti tute a continuous rotary coal feed screw structure which may be of any desired length and may be driven from an end thereof, as hereinafter set forth;

Bearing I59 includes a head I59a carrying a journal bushing I 59b for the hub I59d of sprocket 239 which bears against thrust ring I59e. A suitable outlet I59e for material passing ring I59e may be included.

To provide for supply of air to the burning fuel, inlet air chamber I6I surrounds the pot wall I53, formed by bottom wall I62 and outer wall I63 and generally open at the top.

A suitable upper margin for the pot I52 is provided preferably in separable form and is generally referred to as a retort. While the retort may be formed and mounted in various ways, it is advantageous to provide a retort base ring I66 which may perform a number of functions. In

the form illustrated ring I66 is held in position by bolts I61 threaded into lugs I64 on outer wall I63 of air chamber I6I, and may have a sealed engagement therewith by employing an asbestos gasket I68. Base ring I66 may likewise form a closure for the juncture between pot wall I53 and pot liner I54, the form shown in Fig. 7 having an ,for eflicient operation. In the form shown in Figs. 7-9 the retort I12 is provided with an inner wa11 I13 forming a continuation of pot I52 and the inner face of base ring I66, and resting on an asbestos gasket I14 in a suitable depression in base ring I66. The outer wall I15 slopes outwardly and downwardly to the grate structure, and rests on an asbestos gasket I16 in a suitable depression in base ring I66. The retort crown I11 provides an integral smooth curve between walls I13 and I15, and is preferably relatively narrow to prevent retention of material thereon.

Suitable tuyre openings I18 extend through the retort I 12 at appropriate points. It has been determined that with the arrangement described the most advantageous construction comprises provision of a series of tuyeres I18 adjacent the upper part of the inner retort wal1 I13, preferably sloping slightly downward, and a smaller number 4 of tuyeres I18 extending through the upper part of the outer retort wall I at about the same level. The retort I12 is held in place by'means which preferably permits its ready removal and replacement, such as hooks I19 which maybe cast integral with the retort walls I19 and I15, and which engage the lower face of the retort base ring I66 through suitable retort lock openings I88.

The rotary grate structure located around the retort I12 is adapted to receive the burning coal and ashes which flow outwardly over the retort, sifting the ashes into a suitable annular receiver in which they are carried around the burner to a point of discharge. The various parts are carried by a rotor ring I8I which is rotatably mounted on the pot I52. The mounting of rotor ring I8I on ball bearings is such that the parts may be readily assembled, the bearing will be easily accessible and the structure will function smoothly under the substantial variations in temperature and consequent expansion and contraction of the parts encountered under these conditions, the ball race being formed by cast surfaces.

rotor ring I8I. An upwardly beveled flange I83 on wall I63 and a downwardly beveled flange I84 on base ring I66 are arranged to provide a ball race groove I85 cooperating with groove I82 to retain the balls I86. By the removal of retort base ring I66, the balls I86 will be readily accessible; and as the faces of grooves I82 and I85 are substantially at 90 to each other, their spacing permits smooth unobstructed travel of the 1;

balls under various conditions of expansion due to changes in temperature.

The outer margin of the retort base ring I66 is provided with an apron I81. extending outwardly and downwardly over the upper edge of the rotor ring I8I,.apron I81 providing a smooth path of flow for ashes around the ball bearing structure and beyond the outer face of rotor ring I8I, the adjacent faces of apron I81 and rotor ring I8I being suitably shaped to provide a relatively slight clearance and prevent substantial amounts of ashes from reaching the balls I86, the opening I49 below said balls permitting any ashes or the like to fall out of the raceway. The annular pocket 233 below apron I81 accumulates ashes and an inner seal of ashes 234 is formed at the lower edge of the apron, restricting the passage of air to the space above the grate.

In the embodiment shown in Figs. 7-9 a grate ring I88 is utilized, removably mounted on rotor ring I8I and adapted to receive removable grate segments I89. These segments are preferably flat integral castings provided with an inner V flange I98 extending into close relationship to retort basering apron I81. Suitable slots permitting ashes to pass the segments I89 include;

the radial slots I9I, restricted marginal slots I92 direction of rotation, and the spaces left between the periphery of each segment I89 and the ad- The arrangement comprises a ball race groove I82 in the inner face of the upper partvof on the advance end of each segment I89 extends beneath a locking lug I96 formed on the upper edge of grate ring I88. Grate ring I88 may extend to .a point higher than the lower edge of apron I81, the intervening, space normally filling with ashes which form the air seal across the narrow slot between the apron margin and ring I8I.

The grate ring I88 is suitably mounted on rotor ring I8I to permit ready removal without affecting the rigidity and reliability of the mounting under service conditions. A suitable arrangement is indicated best in' Figs. 8 and 10, andincludes beveled wedge'lugs' I91- on rotor ring I 8i engaging beveled wedge lugs I98 on grate ring I88 to force the grate ring downwardly into proper position by rotating it relative to rotor ring I8I; stoplugs I99 on rotor ring I8I and removable locking slugs 288 fitting between stop lugs I99 and wedges I91 when the grate ring I88 has been turned into proper position.

The grate rotor structure is preferably provided with an ash table 284, receiving ashes which pas the grate segments I89 and conveying su-ch ashes to a point of discharge. A plurality of ash table segments 285 form a continuous annular platform around rotor ring I8I adapted to receive the ashes. Each table segment 285 is provided with an inner flange 286 extending inwardly and upwardly, resting on an annular shoulder 281 on rotor ring I 8|, the abutting edges of the table segment 285 being in overlapping relationship to provide continuity and accurate registration. The lower rim 288 of grate ring I88 bears against flanges 286 and securely locks the table segments 285 in firm fixed position when wedge lugs I91' are forced in flange I98, preferably angled inwardly in the against wedge lugs I98 as above described. Table segments 286 may be accurately located by positioning lugs 28I on'rotor ring I8I engaging corresponding positioning recesses 282 in segments 285.

An ash trough extends around and below the ash table segments 285, for the direct discharge of ashes from the ash table. The ash trough 289 (Figs. 7-9) has an outer wall 2I8, a bottom 2 extending beneath and slightly spaced from the table segments 285, and an inner flange 2I2 extending upwardly substantially beyond the lower face of table segments 285. Segments 286 are preferably provided with diagonally tangential ribs 2I3 which serve to plow outwardly toward wall 2I8 ashes which fall between ash table 284 and wall 2I8, preventing the ashes from escaping over flange 2 I2 while avoiding any engagement between the rotating and fixed parts. The ashes brushed outward by the ribs 2I3 accumulate at the outer edge of the bottom plate 2 and form an outer ash seal 26I at the periphery of the table 284 so as to restrict the flow of air to the space above.

The ashes carried around by ash table 284 are continuously discharged by a simple scraper arrangement (Figs. 7 and 8) including an ash plow or vertical plate 2 on the outer wall 2I8 of the ash trough extending into juxtaposition to the ash. table 284 and grate ring I88 and de- (Figs. 8

the junctions of the segments 2l9 and remo ably mounted on theburner body I50 to permit convenient mounting and disassembly of the ash trough m.- The remaining/junction -between segments 2I9 overlying lfe coal feed tube 10 22 is supported by a brac body I50, provided a detachable clamp 222 overlying the i ction and which may be detachably fas'tened' to the bracket 22I.

The upper margin of the ash trough 209 is connected to the furnace body to close the space between the body and the burner unit. This may be accomplished by providing a closure 1; 22I on the burner v .plate 224 resting on shoulder 225 formed at the upper margin of outer wall 2I0' of the ash trough, and extending outwardly to the furnace walls. A suitable filling or lagging 226, such as furnace cement or the like, may be employed -'to fill the spaces between plate 224 and the furnace walls, which in Fig. 6 are shown as comprising the usual water leg 221 of a domestic furnace. Plate 224 may be locked on shoulder 225 by segmental locking plates 228 fitting into an annular recess 229 in the upper margin of the outer wall 2") of' the ash trough and provided with a longitudinal rib 290.

The mechanism for rotating the grate unit employs an intermittent drive, imparting a periodic impact to the rotating structure, as such an arrangement serves to break up the fuel mass and to facilitate the sifting of the ashes and small clinkers through the grate. In the construction shown in Figs. 5 and 11 the shaker rod I09 extends beneath the ash trough 209 and is pivotally connected at its ends to the lower end of a feed dog arm 2 extending upwardly between the air chamber I6I and the grate rotor ring IN and having at its upper end a feed dog 242 projecting laterally. between the support flange 243 on the inner face of rotor ring I8l, and rack' 244- on said ring overlying flange 243. 'The feed dog 242 is provided with a rocking face 245 riding on flange 243, and suitable teeth 246 at its forwardend adapted to engage rack 244. The arrangement is such that when the shaker rod I09 is shifted to the left ,of Fig. 5

the dog 242 will be rocked on face 245 until teeth rection by continued travel of the grate rotor ring I8I under its own momentum or by the 246'engage rack 240, further movement of the shaker rod I09 serving to rotate ring I8I and the grate parts mounted thereon, while ring I8I will be free from dog 242 at the end of such stroke and during the return stroke of shaker rod I09 owing to the disengagement of teeth 246 when the dog 242 is rocked in the reverse diretum travel of shaker rod I09.

To prevent reverse rotation of the grate ring 'I6I .and-associated'parts a detent dog 241 is provided on detentarm 248 pivotally mounted on '6 stud 249 on the'burner body I50at any convenient circumferentialpoint and held yieldably in operative position as by counterweight 260.

Figs. 11 and. 12 show the air supply and control system between the blower 18 and the burner and 9) by bracket legs 220 overlying a 'of housing 265 to form a 70 unit C, The volume ofair from; blower 13 is suitably regulated, as-by butterfly-damper 264 {mounted in air control housing .265 on spindle 2 preferably provided with suitable locking; means, the form illustrated having a locking disc 75 1118 screw 29I. An elevator screw-292 is posi- Y :61 mounted on the end of spindle m a the rear of housing 265 (Fig. 3) and held in adjusted position by locking knob 266' threaded on screw stud 289 extending through concentric slot 210 I These functions may all be performed by a single mechanism comprising a valve flap 21I fixed to pivot spindle 212 located in the upper part of a section of the air control housing 265 in advance of damper 264 and engaging valve seat 213, which is preferably inclined in the direction of air flow from the blower. The end of spindle'212 may be bent downwardly outside pointer 214-serving in conjunction with suitable marks 215 or the like on the outer face of housing 265 to indicate the position of flap 21I. c

To arrest'valve flap 21I at a predetermined preferably variable distance from seat 213 we provide a natural draft regulator spindle 216- threaded in housing 265, provided with a laterallylextending stop arm 211 within housing 265 positioned for engagement with the face of 2H j'and serving as a variable stop for arresting the" downward movementof flap 21I at any point between thevalve seat 213 and the maximum desired opening of flap 21I by rotation of spindle 216 by-means of knob 218, spindle 216 being frictionally heldin adjusted position as by spring washer 219.

The air control housing 265 is connected to a suitable air duct 280 running to air inlet chamber 28I (Figs. 8 and 11) in the burner body I50, and merging, around the casing for the coal feed passage, with the air inlet chamber IN to provide a generally tangential air feed adapted to distribute the air evenly throughout the air chamber I6I and thence to tuyres I18.

A suitable arrangement is provided for automatically removing the ashes from the burner unit C and discharging them at an appropriatepoint, the construction preferably including an ash removal conveyor and an elevator for transferring the ashes from the conveyor to a suitable. discharge point. In the form illustrated the ashes are removed from the ash discharge chamber 2" (Fig. 9) by ash removal tube 295 mounted in the burner body I50 and forming a continuation of chamber 2I1. Tube 285 extends to an appropriate point and is shown as terminating adjacent drive unit B (Figs. 1 and 3). At this point a suitable elevator unit D is positioned to receive the ashes. A convenient construction is disclosed-employing an arrangement in'which the ash removal tube 265 terminates in an alevator pocket 281 (Figs. 13 and 14) formed in elevator base 288. Ash removal screw -2I8 termij, nates at the pocket while the. shaft 39 onwhich the screw is mounted extends through the pocket and a suitable bearing 269 at the opposite side of the elevator base 288, and thence to the drive mechanism as already set forth. An elevator tub 290 ismounted in elevatorv base 298 extending from pocket 281 upwardly in.

any desired direction to permit discharge at any apropriate point dictated by local conditions, the angle of tube 290 being readily adjusted by clamping base 288 in any desired rotated positioniabout ash removal tube 265 through clamp tioned in tube 298 to pick up ashes discharged into pocket 281 and raise them in tube 298 to a discharge at the upper end of the tube. Various methods of mounting and driving screw 292 may be employed, and preferably are arranged to permit accessibility and removal of screw 292 without dismantling the supporting and driving arrangement. In the form illustrated, the screw 292 is driven from a bevel gear 293 on shaft 89 driving bevel gear 294 mounted on elevator base 288 and carrying sprocket 295 which through sprocket chain 298 drives sprocket 291 on elevator shaft 298 mounted in thrust bearing 299 in the elevator base 288.

Means may be provided for protecting thebetween the upper end of sleeve 388 and shaft 298, and leaded bronze bushing 283 between the'lower end of screw 292 and tube 388. A suitable sealing bearing is provided between the lower end of screw 292 and the base'288 and comprises a leaded bronze thrust washer 385 and a suitable resilient backing such as rubber rings 388 surrounding shaft 298. To aline the bearings at the ends of shaft 298,

a suitable self-alining joint is provided, such as that illustrated in Fig. 13, in which the lower section of shaft 298 is provided with a tongue 383 held in a corresponding slot 384 in the upper section by pin 385, the construction being arranged to permit the very slight play necessary to assure smooth running in the bearings.

Screw 292 will of course be broken at the flexible connection as shown.

A suitable discharge arrangement is provided at the upper end of elevator tube 298. This may comprise a discharge head 388 mounted on the upper end of elevator tube 298 and carrying an upper bearing 381 for the elevator shaft 299. Head 388 is provided with suitable spout discharge means, the illustrated construction employing two discharge spouts 388 and 389, each of which may be provided with a flexible tube 3"! clamped thereto for directing the ashes to any suitable receptacle, such as ash can 3" (Fig. 1). A suitable hinged door 3I2 may be provided opposite spouts 388 and 389 to permit access to the mechanism and to serve as an overflow outlet for ashes whenthe'spouts 388 and 389 are filled or obstructed.

A suitable arrangement is provided-for driving the coal feed screw 2I from shaft 85. In the arrangement indicated in Figs. '1, 9 and 11 shaft 89 extends through a bearing 235 in chamber 211 and bearing 238 on bracket 231 On burner body I58, and drives coal feer. screw 2| through sprockets 238 and 239 (on shafts 89 and I88 respectively), and sprocket chain 248.

A modified burner construction is shown in Figs. 15 and 16. In this arrangement the retort I12a is provided with a depressed portion 258 immediately below the inner tuyres I18 to facilitate the introduction of the atively higher, the outer retort ing a relatively sharp downward slope toward the and is rei- I151: hav-- grate. Retort I12a is held in position by locking hooks 25I on the retort base ring I88a engaging crossbars 252 in retort; I12a. Thegrate segments I89a; are mounted on studs I940, carried directly by the rotor ring I8Ia and extending through the top of sockets I93a, the segments I89a resting on suitable flanges 253 at the base of studs I980.

The ash table 2840 is mounted directly on rotor ring I8Ia. and is arranged to retain the ashes.

by including an upwardly extending lip 25l.at its outer margin, dispensing with the use of an ash trough. Mounted in place of such trough but in the same general-manner is a conical ash hopper wall 255 having its lower rim 258 ex'- tending downwardly inside lip 254 and provided with diagonal ribs 251 on its lower face arranged to plow inwardly ashes which tend to work beneath rim 258 toward lip 254. The ash hopper wall 255 may be arranged and supported in the same manner as the ash trough 289, but legs 228a and bracket '22Ia may carry detachable retaining clamp members 258. Ash table 284a may be provided with suitable means, such as ribs 259 extending upwardly around lip 254, which may be engaged by a poker or other suitable implement for manually rotating or shaking the grate structure.

A somewhat different ash discharge arrangement is employed with this modification, the ash plow 2Ila. having an advance portion 282 curved upwardly and outwardly .to convey ashes accumulating on table 284a over lip 258 into the discharge passage 283 communicating with ash discharge, pocket 2I8a.

While various proportions and designs may be employed in the different parts of the apparatus disclosed herein, the proportions are of importance in various parts, and particularly in the burner structure, the size and proportions of the pot, retort, grate segments, ash; slots in the spacing thereof, having been determined after substantial experiment as adapted to most eflicient operation with coking'bituminous coal; and the drawings herein are drawn to scale to show the proper dimensional relationships between the various parts.

A suitable electrical control arrangement (not shown) is provided, and may be ofthe type in which the motor 15 is operated at full speed at suitable intervals, though the invention is not necessarily restricted to a control of this type.

Under certain circumstances, and particularly when burning certain types of coal, gases may be forced back through the. coal feed tube 22, and an arrangement is provided for preventing the escape of such gases. Such an arrangement may include a trap in which the gases will collect, and means for conducting the gases from the trap to a suitable discharge. In the preferred arrangement the gases are conveyed to the burner. Owing to the relatively low velocity 0f.such gases it has been found that under.

certain conditions there is a tendency for flne solid particles to accumulate in the return pipe and eventually to clog the pipe. The preferred formtherefore includes means for preventing such accumulation of dust and the like, and for returning the gases to the burner or elsewhere by positive means, such as a suitable supply of air, which may be taken from the blower system.

An arrangement of this type is embodied In the preferred form illustrated herein, and is shown best in Figs. 3 and 6. It includes a fresh air connection I35 with the outlet offblower 18 the gas pocket I39 formed in the upper face of the coal feed passage 13 in base 12. The fresh air connection I35 thus utilizes a higher pressure from the blower than can be found anywhere beyond the damper control. A gas return pipe I40 extends through the other side of pocket I39 in alinement with nozzle I38 and spaced therefrom by a distance suitable forobtaining an injector effect under the conditions of air pressure and dimensions employed in the arrangement; The gas return pipe I" is connected to the burner unit C in a manner hereinbefore set forth. Gas pocket I39 is sealed by a removable cover MI.

While the apparatus is adapted for use with various types of coal it has been particularly designed to solve certain" special problems encountered in the burning of bituminous coal, which has special characteristics affecting its collection, transportation and combustion.

Proper feeding of the coal is highly'impor tant, for the purpose of assuring proper burner operation, for economy in driving the feed screws, and to avoid the jamming of the feed which has heretofore been a prolific source of trouble in apparatus of this type. A feature of the present arrangement involves keeping the feed tube 22 substantially less than full of coal,

and preferably about half full.

The arrangement likewise permits the use of screws driven in the same direction, permitting the employment of a single type of screw for the entire feed. The connection between the feed shaft sections comprising a stub shaft connecting the hollow ends of the shaft sections furnishes a flexible joint easily assembled in the field and offering very little restriction to the flow of the fuel. All of the screw sections comprising the entire coal feed system are under tension from any pressure whatever on the surfaces opposite the coal feed tube discharge. The reverse screw maybe arranged to impel coal continuously away fromthe feed screw bearing, which may therefore be of any desired type. The elimination of the tendency to pack the fuelin throat I5I furthermore permits the maintenance of fuel feed in tube 22 at substantially less than the full capacity of the tube as already indicated, since substantial back pressure on the fuel at the burner owing to the resistance caused by forcing the fuel upward under previous conditions causes the coal to back up along the feed screw; and even if feeding at less than coal tube capacity is attempted,s'ubstantial back pressure at the burner and the resultant accumulation of coal in the tube will make it impossible to operate the feed.

tube 22 partially filled at any point within a substantial distance of the burner. With the construction illustrated however the feed tube is filled for. only a short distance from the burner, an arrangement which notonly reduces to a, minimum the power necessary for feeding at this most exacting point, but which is also desirable since a full feed tube 22 for a short distance from the burner is serviceable in forcing the gases to travel upwardly through the burner and not back through tube 22.

In burner 'retorts of the prior art difficulties have been encountered because of the tendency of the coal under certain conditions to burn down in the pot toward the feed screw, resulting in the formation of coke and clinkers whichobstruct the feed and burning of the coal and may result I in breakage or stoppage of the mechanism. The

beginning to end, preventing buckling of the sections and tending to keep all parts in alinement.

The burner unit C is particularly designed to provide thoroughly eflicient combustion both under active operating conditions during coal feed and operation of the blower,-and under banking conditions. There is also secured a careful balancing between the rate of coal feed, the rate of air supply and the combustion characteristics of the coal, both as to the time required to burn to ash and the volatilization of combustible-gases. The latter problem is especially important in the burning of bituminous coal, and involves likewise the formation of coke, which heretofore has been a source of serious difficulty and obstruction due to the tendency of the coal to coke back into the feed zone, interfering with the operatic-n of the feed mechanism and frequently causing complete stoppage of the machine. The design also contemplates the efi'ect of oil which is frequently used for dust-prevention.

The rotating element I51 provided at the side of the throat opposite to the discharge end of the coal feed tube serves to prevent the coal from forming a packed mass at this point, and thereby increasing notably the facility with which it may be forced upwardly by the horizontal pressure of the feed screw. In one sense it may be said that this auxiliary screwincreases the relative fluidity or flowing qualities of coal at this point. In the preferred form the rotating element is in the form of a reverse screw exerting a counterbalancing horizontal pressure on the coal discharged by the feed screw while likewise preventing the foratravel of the coal upwardly in the pot may like-,

wise be obstructed by the formation of clinkers and the like which adhere to the pot walls, and by mechanical obstructions provided by the wall surfaces. In the present construction a retort is provided in which the zone of active combustion is restricted to the upper portion, and which extends downwardly for a suflioient distance below the lowest point of air supply so that the fire will not reach the region where formation of clinkers, coke and the like will interfere withthe feed mechanism. Any clinker formation developing will be prevented from adhering to the pot by. the smooth liner I54 but will be forced upward and broken up by the incoming coal.

Under full draught conditions the relation between the coal feed and the rate of'combustion is such that the burning fuel overflows gradually across the retort I12 and over grate segments I89, and mayreach the walls of the furnace. The relatively slight projection of the retort I12 above segments I89 facilitates the lateral flow, and is particularly advantageous in bituminous coal combustion in which the incandescent coke is more or less fluent,- the arrangement permitting the formation of a relatively wide thin fire which produces maximum eillciency, rather than .a high,

sure full combustion of gases which pass upwardly from the coking zone andprovide an adequate supply or air for full combustion, the outer tu- S'iges in wall I15 assisting if necessary in the mation of a solidly packed mass of coal, the result being. that the coal will travel upward as v gradually as may be desired without exerting combustion of the portion of the fire outside of the retort I12. The spreading of the fire is, facilithe upper part of retort I12 limited in depth by I the distance that air will penetrate from tuyeres I18. This arrangement, limiting the bank tuyre to a zone at the top of the pot substantially spaced from the feed worm 2|, eliminates the possibility of coking back under banked conditions, aser-ious difliculty with prior arrangements. At the same time a small zone of definitely buming fuel is maintained so that when the drive unit is again started and the coal feed is resumed, there will be no difficulty about kindling promptly the green coal that is more or less abruptly forced upwardly in the pot I52.

When operating under banking conditions air is drawn through the tuyeres I18 by the ordinary stack draught in a manner similar to the operation of hand-fired coal furnaces. This is made possible by the action of stop arm 21! which holds valve flap 2'" open to the proper extent, thereby permitting the maintenance of a minimum bed of burning material without risking the extinguishing of such bed by insufficient air, sudden influx of fuel or the burning out of accessible fuel by excessive draught.

The arrangement likewise is adapted to minimize the tendency to form coke in the lower portion of the pot where it might interfere with screw 2| through the depth of the pot, the aircooled walls and the double-wall construction. If however coke should form in throat Il, it would notwedge between the screw and the end of the feed passage. as in prior arrangements, but would tend to be broken up bythe rotary action of the feed screw 22 and reverse screw I51.

The rotary ash collecting unit is arranged to remove accumulations of ashes with a minimum disturbance of the fire bed. This operation is facilitated by the smooth-surfaced grate segments I89 and the intermittent shaking action imparted thereto. The formation of .the described type of fire bed likewise facilitates the scouring of fine clinkers from the retortl'lZ and their discharge on to segments I89, which may be provided with slots'sufliciently large to receive the small clinke'rs as/formed and to maintain a clean fire even under conditions which operate the burner at infrequent intervals. The

ashes are effectively sealed in the ash receptacle and readily discharged from the burner in a manner already indicated.

Any gas which is formed will normally be generated so high in the pot- I52 that it will tend to flow upwardly and to be burned; but in case gas is forced back through coal feed tube 22 it will be positively returned to the ash pocket ZIB by the action of'tjet noz'zle I38, and will pass upwardly to combustion past the grate segments I89, This arrangement will also provide a slight air feed outside of the retort I12 which will be operative to some extent when the blower 18 is not running, since the natural flue draught of the furnace will exert a certain suction effect on the gas return pipe- I40. This arrangement also prevents any tendency for'dust to collect in the gas return line. It may be noted that when the valve flap 2'" is allowed to fall upon its seat it provides positive means for preventing gases from the combustion zone from returning' through the blower structure, if conditions should arise that demand such an arrangement.

The operation of the arrangement for conveying the ashes to a suitable point of discharge will be apparent from the detaileddescription. The construction is such that the ashes may be discharged at any desired point, and are kept completely housed in conveniently located conveying tubes.

The drive, operated by a single motor and compactly arranged, is constructed so that theblower may be operatedwithout the coal feed, which may at times permit operation by hand firing in cold weather pending repairs to the coal feed mechanism. .The clutch 93 is likewise arranged to permit throwing in the coal feed and ash removal mechanism abruptly after motor 15 is up to speed, exerting a sudden impulse that may be valuable in dislodging a slight obstruction. The apparatus is likewise arranged so that the motor I5 will be stalled before breakage of any of the drive parts, allowing the electrical system to throw out the motor circuit and take care of emergency conditions without damage to any part of the machine. This result is accomplished partly by the strength and simplicity of the construction, partly by the use of especially strong feed screws, and to some extent by the use of a special thrust bearing 388, which serves to take a substantial part of the stress caused by an obstruction to the conveying mechanism thereby reducing correspondin y the maximum stress on such mechanism, without materially reducing thepower transmitted from the motor I5 under normal conditions.

The blower structure has been carefully arranged to give rapid and accurate control of an adequate supply of air at all times without the usual excessive intake noise.

The air supply for the fire is intended to come mainly from the tuyre openings of the retort walls I13 and I15, and this supply serves in addition to maintain a proper cooling of the retort. Where there is an insufficient supply of air through the retort, there is a tendency for these parts to overheat and cause an improper coking and clogging of the rising column of coal. It is therefore desirable to control the other sources of air to the space above the grates and the inner and outer ash seals above described, or some other suitableregulation of the air supply below the grate, should be provided. Under running conditions not over 50% of the total air supply should enter through the grates and under bankin conditions this should be further reduced. a

All of the screw parts picking up the coal from the bin and delivering it to the retort are retamed under tension in operation, preventing buckling of the sections and keeping all of the 

